1. Field of the Invention
This invention relates to the field of fullerenes and more specifically to the field of biochemical sensors comprising chemically sensitive field effect transistors having nanotubes.
2. Background of the Invention
An increasing interest has occurred in the development of chemical sensors in the identification of biological molecules or fragments. Such an increasing interest has been seen in a wide range of industries including clinical chemistry such as alternative site and critical care measurements, environmental detection of hazardous and mutagenic substances, in-line monitors for the food production industry, gene expression, and the like. For instance, determination of gene sequences is typically based upon spectroscopic characterization of dye molecules that are tagged to specific recognition molecules. The characteristic spectrum of the dye molecule detects binding of the dye molecule to a biological fragment such as DNA. Drawbacks of using the spectroscopy technique include limited sensitivity and selectivity of the technique.
Chemical sensors with enhanced sensitivity have been used for detection in such industries. A typical chemical sensor device is a chemically sensitive field effect transistor (chem-FET). Typical chem-FET devices have relied on the use of a porous dielectric layer into which a substance such as a chemical to be detected is absorbed. The dielectric constant of the dielectric layer is altered by such absorption, which results in a positive detection of the substance. Drawbacks to chem-FETs include a susceptibility to moisture. For instance, a dielectric layer sufficiently porous to allow for DNA will typically also allow water into the gate of the chem-FET, which can result in failure of the device. Consequently, chem-FET devices having carbon nanotubes have been used for such detection. The carbon nanotubes are usually used as a bridge between the source and the drain. The presence of certain molecules such as oxygen or ammonia can alter the overall conductivity of the carbon nanotube by the donation or acceptance of electrons. Selectivity in the carbon nanotubes is typically achieved by functionalizing a majority or all of the surface of the carbon nanotube through the placement of specific functional groups on the nanotube surface, with such functional groups having the ability to selectively bind specific target molecules. Drawbacks of such chem-FETs comprising carbon nanotubes include functionalization changing the electronic properties from that of a semiconductor to that of an insulator. Further drawbacks include the diversity of tube diameters, chiral angles, and aggregation states of the tubes.
Consequently, there is a need for a more efficient chem-FET having improved selectivity and sensitivity. Further needs include a chem-FET that is not susceptible to damage by absorption of water through the dielectric layer. Additional needs include a chem-FET with carbon nanotubes that maintain their semiconductivity.